Comparison between models of the decay of light compound nuclei

Abstract

The decay of the compound nucleus is traditionally calculated using one of two types of statistical models, either a sequential or a simultaneous emission one. The best known sequential emission models are the Weisskopf-Ewing one and the Hauser-Feshbach one. Both sequential emission models emit only one particle at a time. A well know simultaneous emission model is the Fermi breakup one, which takes into account the fragmentation of the compound nuclei into two, three or more residual nuclei/particles. We have compared the particle and residual nucleus distributions of the Weisskopf-Ewing and Fermi breakup models in the case in which only stable nuclei/particles are emitted. We find that the Weisskopf-Ewing results in larger yields of light particles and heavy residues than the Fermi breakup model, while the latter results in larger yields of intermediate mass fragments.

Fermi breakup and the statistical multifragmentation model

“…where ρ 0 and ρ c are the level densities of the initial and residual nuclei, respectively, Q c is the Q-value of the reaction and σ c (ǫ c ) is the absorption cross section for particles of type c incident on the residual nucleus at energy ǫ c . This implies an average relative energy for emission of particles of type c of 2T c + V c , where V c is the effective Coulomb barrier between the emitted particle c and the residual nucleus and the temperature T c is very close to the temperature T 0 obtained from the same two-body decay in the FBM [27]. Judging from the energy released by the two-body decay mode, we would thus have to conclude that the FBM/SMM emission is no more explosive than the CN one.…”

“…As the total excitation energy is increased, other particle-unstable excited states that are long-lived in comparison to the initial decaying nucleus could also be included and can make significant contributions to the phase space integral [27]. These can be incorporated compactly using the densities of excited states of the fragments.…”